1. Field of the Invention
The present invention relates to spas and hot tubs and, more specifically, to a water circulation and heating system that utilizes a low flow rate water pump.
2. Description of the Related Art
Water circulation and heating systems for spas and hot tubs generally fall into one of two categories: 24-hour dual pump systems and 2-speed single pump systems.
In 2-speed single pump systems, a single two-speed pump is used for water circulation, which includes filtering and heating of the water, and for powering the high speed jets that are typically turned on when the spa is in use. The low speed is used to circulate the water for the purposes of heating and filtration, and the high speed is used to power the high speed jets.
Current two-speed pump systems use a high Wattage motor (typically 598 Watts or higher) which, at its low speed setting, circulates the spa water at a flow rate of approximately 15 gallons per minute (gpm) (57 liters per minute (lpm)). At its high speed, the pump circulates the water at a flow rate of between 60 and 120 gpm (227 and 455 lpm). As the spa water is circulated, it is filtered, chemically treated and heated. The heating is accomplished with a heater, which typically comprises an electrical heating element inside a cylindrical housing. Although some earlier 2-speed pump systems utilized vertically mounted heaters (in which water flows through the housing in a vertical direction), modern systems opt for horizontally mounted heaters, such as the one described in U.S. Pat. No. 4,924,069, entitled "HOT WATER SUPPLY FOR TUBS", issued May 8, 1990 to Attillo G. Giordani. Horizontally mounted heaters are generally preferred in the industry because head loss (pressure loss) problems are encountered when water is forced through a vertically mounted heater, especially at the high water flow rates used in two-speed pump systems.
Another problem with 2-speed pump systems is the pump's high power consumption. Even at its low speed setting, the 2-speed pump's power consumption is high enough to make it impractical to run continuously. As a result, 2-speed systems are configured so that the spa water is circulated intermittently over a 24 hour period (typically only 5 hours over a 24 hour period). The intermittent circulation periods can be initiated by a timer or manually. When the spa water is not being circulated, it can become dirty from lack of filtration and its temperature goes down from lack of heating. Furthermore, 2-speed pumps are relatively noisy, which may make the spa systems that incorporate them unsuitable for certain areas of the home (such as bedrooms).
With 24-hour dual pump systems, two separate pumps are used in two separate circulation systems. A low speed pump is used to circulate the spa water through a low speed circulation system that is used for heating and filtration. A second high speed pump is used to circulate the spa water through high speed jets in a separate high speed circulation system when the spa is in use. The low speed pump consumes less power and produces less noise than the 2-speed pumps described above. As a result, it may be operated continuously so that the water is continuously filtered and heated, and it may be located in noise sensitive areas of the home.
However, the low speed pump circulates the water at a flow rate of 15 gpm (57 lpm) or less, which causes problems with the horizontally mounted heater that is used to heat the water. It is common for some amount of air to make its way into the circulation system. The air eventually propagates to the heater housing, where it becomes trapped because the low speed pump does not generate enough pressure to force the air out of the heater housing. The air lowers the water level in the heater housing, which can expose portions of the heater element. The exposed heater element portions become much hotter than the submersed portions, and this can cause the heater element to overheat and fail. In addition, although the continuous filtering of the spa water at flow rates of less than 15 gpm (57 lpm) is sufficient for keeping the water clean when the spa is not in use, a higher amount of water filtration is desirable when the spa is in use.